The variety of rock movement has baffled scientists for decades. 8Some rocks seem to roll as they move forward. 9Some take unexplainable routes. 10Large ones have traveled past small ones that have stayed still. 11Some scientists suggest that the rocks are pushed by wind. 12Others believe they slide on small amounts of ice or mud. 13So far, research has not confirmed any theory.

  Which sentence best identifies the main idea of paragraph?

  a. Scientists are baffled by the different ways the rocks move.

 b. Scientists are confused by the different ways the rocks move, and theories involving wind, ice, and mud have not been confirmed.

 c. Scientists have theories of how the rocks move.

 d.  The rocks have stumped scientists because some roll, some take unexplainable routes, and some have traveled past ones that have stayed still, but scientists have theories that the rocks are pushed by wind or that they slide on ice or mud.